1. Field of the Invention
The invention relates in general to a slant reflector with a bump structure and a fabricating method thereof, and more particularly to a slant reflector with bump structure applied in a reflective type liquid crystal display (LCD).
2. Description of the Related Art
In the recent years, not only the brightness but also the viewing angle has become importand for reflective type liquid crystal displays (LCD) in the commercial market. How to develop a reflective type LCD with high brightness and a wide viewing angle is a very important issue for the manufacturers and researchers.
FIG. 1 represents the reflectance distribution of a conventional reflector. The reflectance is measured by an optical detection system. The reflector is set up horizontally, and surface thereof is smooth. It is assumed that an angle of incidence of the incident light arriving at the surface of reflector is 20 degree. According to optical theory, the angle of reflectance of the reflected light is −20 degree. Hence, the maximum reflectance R1 occurs at the viewing angle of −20 degree, and the curve of reflectance distribution is very narrow, mostly in the region around −20 degree, as shown in FIG. 1.
However, the ideal LCD should represent the maximum reflectance at a viewing angle of 0 degrees, and distribute portions of the reflected light at a wide range of the other viewing angles. To shift the curve of FIG. 1 towards the left, another conventional way is to slant the reflector for changing the light path. For example, the reflector can be slanted until the angle between the surface of reflector and the level is 10 degrees, so that the original incident light at 20 degree of incidence can be reflected at the angle of 0 degrees, as demonstrated in FIG. 2. FIG. 2 represents the reflectance distribution of another conventional reflector. The reflector is set up with an inclined angle (10 degrees), and the surface thereof is smooth. The maximum reflectance R1 occurs at the viewing angle of 0 degrees, but the curve of the reflectance distribution is still narrow, mostly in the region around 0 degrees. The objective of the reflective type LCD with wide viewing angle has not been achieved.
In order to solve the problem, in which the reflectance over concentrates at a certain angle, a further conventional way is provided by forming numerous bumps on the slant reflector. FIG. 3 represents the reflectance distribution of a further conventional reflector. The reflector is set up with an inclined angle (10 degrees), and there are numerous bumps formed on the surface of reflector. A high reflectance is detected around the angle of 0 degree due to the slanted reflector. Also, parts of reflectance are detected in a wide range of viewing angles since the normals on each point of the bump are not parallel. Comparing the results of FIG. 2 and FIG. 3, the maximum reflectance R2 of FIG. 3 is lower than the maximum reflectance R1 of FIG. 2, but the reflectance distribution of FIG. 3 is wider than that of FIG. 2. Therefore, an LCD adopting the slant reflector with bump structure possesses two attractive features—high brightness and a wide viewing angle. A conventional process for making a slant reflector with a bump structure has been presented. In this conventional process, a photo-mask with a single slit is provided, and multi-step exposure is performed. First, a photo-resist on the substrate is exposed to UV (Ultraviolet) light at an intensity of L1 for a time t1, and an exposed area A is formed. Second, the photo-mask is shifted, and the photo-resist is exposed by the UV light at an intensity of L2 for a time t2, to form an exposed area B. Then, the photo-mask is shifted and the exposure is performed, as depicted before. The steps are repeated. Either by setting equal the exposing time and the light intensity L1>L2> . . . , or by setting equal the intensity and the exposing time t1>t2> . . . , the size of exposing areas are controlled at the order of A>B> . . . Subsequently, the photo-resist is developed to form a ladder-like look. Then, the ladder-like photo-resist is heated to make it reflow, and becomes a bump with a smooth surface.
However, the conventional process for making a slant reflector with a bump structure has drawbacks. For example, the photo-mask needs to be shifted over and over again. Also, the position of the photo-mask, UV light intensity or the UV duration time needs to be adjusted while the photo-mask is shifted. It is very time-consuming, and the production cost is consequently raised. Furthermore, forming a bump with an inclined angle requires moving the photo-mask and exposing for several times. In a practical application, numerous bumps are demanded for forming a rough surface of slant reflector, so as to enhance the light scattering effect. Hence, the conventional process is not suitable for the mass-production-scale.